Energy Transfer & Transformation — Drills · Grade 8 Science

Chapter: Energy & Heat Transfer

What these drills covers

By the end of Energy Transfer & Transformation you should be able to:

8 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: energy transformation, energy transfer, chemical energy, electrical energy, model, evidence, system boundary, assumption.

Problem 1

A torch converts chemical energy mainly into
  1. light and thermal energy
  2. sound and nuclear energy
  3. mass
  4. gravitational potential energy
Answer and explanation

light and thermal energy

The battery's chemical store becomes electrical energy, then light and heat.

Problem 2

Energy transfer means energy
  1. is destroyed
  2. moves from one place or object to another
  3. is created
  4. disappears
Answer and explanation

moves from one place or object to another

Transfer moves energy; transformation changes its form. Neither creates or destroys it.

Problem 3

A device takes in 200 J and usefully delivers 150 J. How many joules are wasted?
Answer and explanation

50 J

200 − 150 = 50 J, usually transferred to the surroundings as heat.

Problem 4

In a hydroelectric station the main transformation is
  1. chemical to light
  2. gravitational potential to kinetic to electrical
  3. nuclear to chemical
  4. sound to thermal
Answer and explanation

gravitational potential to kinetic to electrical

Falling water's potential energy becomes kinetic, which turns turbines generating electrical energy.

Problem 5

A motor is supplied with 500 J and wastes 120 J as heat. How many joules are usefully transferred?
Answer and explanation

380 J

500 − 120 = 380 J.

Problem 6

Describing energy as 'lost' in a device is imprecise because the energy is
  1. destroyed
  2. transferred to the surroundings, usually as heat
  3. converted into mass
  4. stored in the device forever
Answer and explanation

transferred to the surroundings, usually as heat

It is dissipated, not destroyed — it spreads out and becomes harder to use.

Problem 7

Trace the energy changes from food eaten to a cyclist climbing a hill.
Answer and explanation

Chemical energy stored in food is released by respiration in the cyclist's muscles, becoming kinetic energy of the moving legs and bicycle, and gravitational potential energy as the cyclist rises up the hill. At every step some energy transfers to the surroundings as heat, which is why the cyclist warms up, and some goes to sound and to overcoming friction and air resistance.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Explain why no device transfers all of its input energy usefully.
Answer and explanation

Every real device has moving parts with friction, electrical resistance, or air flow, and each of these transfers some energy to the surroundings as heat and sound. That energy is not destroyed, but it spreads out and is no longer available to do the job intended, so the useful output is always less than the input. Reducing friction and resistance raises efficiency but cannot eliminate the losses.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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